I have a story where the characters are colonists heading to a new planet. My plan is to have the native lifeforms be descended from a single celled lifeform on a comet that shares a common ancestor with earth life. So they'll share traits with us, but be very different.

I want there to be some kind of biochemical incompatibility, but something we could potentially overcome through genetic selection. Since I'm immune to codeine, I thought having a pile of native lifeforms be laced with codeine could work.

I was wondering, does it seem plausible for the native lifeforms (plantlike or animallike) to use codeine as a product of their biochemistry? What role could codeine serve for these creatures? What would be the likely concentration of codeine in the bodies of these creatures?

$\begingroup$Are you immune to other alkaloids, like atropine and morphine?$\endgroup$
– RonJohnMay 27 '17 at 7:33

2

$\begingroup$I don't think so. Most likely explanation is that I lack the CYP2D6 enzyme, which converts codeine into morphine - around 7-10% of Caucasians lack this enzyme. If that's the explanation for me, then morphine and so forth would affect me normally.$\endgroup$
– EttinaMay 27 '17 at 8:24

$\begingroup$Sorry, but starting from bacteria, you shouldn't expect any enzyme found in complex organism to be the same. Quick search revealed that you can't even expect genetic >>code<< (how DNA pairs translate to amino acids) to be same, as there are deviations from so called Universal Code (medicine.jrank.org/pages/2292/…) and depending on origin, entire ecosystem of your planet may be descendant from bacteria which were an exception.$\endgroup$
– M i echMay 27 '17 at 13:40

2 Answers
2

How plausible is that? It depends on what it is used for. That depends on what it can be used for. Reading in Wikipedia, I don’t see any indication of what it does in the plant. I see that it works as a drug by binding to receptors.

So, it could be used as a general-purpose signaling molecule, like a hormone or even a neurotransmitter. Perhaps it has a role similar to serotonin.

Check out this page for ideas. It can be very plausible indeed if it’s used in a similar way as related molecules in Earth life.

One very important factor determining similarities (and differences) between your planet and earth will be the time point at which the single celled organism came from earth to your planet.

If it was a very early bacterium (from when eukaryotes did not even exist, some billion years ago), then more complex lifeforms on your planet will have completely evolved to fit the habitat of that planet. They might still all be prokaryotes or multicellular - in any case they will be vastly different from life on earth. Still, just by random chance they could produce a chemical (which could be codein, but better make something up at this point) that affects humans.
The problem with this scenario is that it feels a bit forced, since - from a biological perspective - the lifeforms on the planet will really just randomly interact with human biology, as there is no reason to assume they produce similar bioactive compounds.

In the case that the single celled organism came from earth to your planet 'quite recently' (from an evolutionary perspective this may still be millions of years ago), then you might be dealing with a simple eukaryote. In contrast to bacteria eukaryotes share many common features, so its is far more likely that a substance that evolved or is used on your new planet also affects humans. While I wouldn't go for codein (which as an opiate is probably only produced by higher plants and not single celled organisms), it's not unlikely that the dominant life on your planet produces a compound that is negatively affecting to all other eukaryotes. Evolutionary this makes sense, as any species producing this compound will have a significant advantage over the other life forms carried over from earth.